Our work has indicated that selected aspects of the electroencephalographic field can, after computer assisted analysis, indicate differences between groups of chronic schizophrenic subjects, normal control subjects and other chronic mental patients. The ongoing EEG, and the EEG related to a non-significant auditory stimulus are investigated under different conditions and using varying analytic techniques. Delta-band power, as indicated by the power density spectrum, is utilized as a measure to equate levels of arousal. Experimental manipulations of arousal are proposed in order to evaluate the efficacy of this measure and the effect of arousal changes on the measured EEG parameters. Findings to date indicate that the chronic schizophrenic subjects may be differentiated by EEG spectral characteristics, the variability of these characteristics, and the auditory evoked changes in electric field pattern. The latter appears to be the most sensitive differentiator, as indicated by the average evoked vector electroencephalogram from the central region of the head. Experimental procedures are proposed to clarify whether the source of excess beta band power in the chronic schizophrenic results from electromyographic contamination. Cross-spectral coherence studies and the character of the cumulative distribution function are being utilized to evaluate the question of local and regional "crystallization" or "noisiness" of cerebral organization. The various electroencephalographic measures are being related to formalized statements of patient clinical parameters in an effort to clarify or delineate nosologic entities. Psychotropic medication and severity of illness appear to affect some EEG parameters. The effect of extended time intervals (greater than 1 year) is being evaluated. The study design utilizes hypothesis-forming and hypothesis-confirming subject groups.